This invention relates to a method and an apparatus in a spinning preparation (fiber cleaning) plant for recognizing and evaluating foreign substances, such as fabric fragments, bands, strings, foil or other thin material and the like in a pneumatically conveyed fiber which has been removed by a bale opener from fiber bales. The apparatus includes an optical sensor device which recognizes foreign substances and which is connected to an electronic control and regulating device.
According to a known method foreign substance recognition is effected subsequent to a preliminary (coarse) cleaning or after a mixing step, that is, prior to a fine cleaning. The fiber tufts are admitted via a suction condenser to a delivery chute, one wall of which is formed by an endlessly circulating, obliquely oriented conveyor belt. Thereafter, the fiber tufts are moved by the belt to an optical recognition system. An evaluating device processes the measurements and if foreign substances are detected, the appropriate sectors of a nozzle bank are activated. The nozzles of a section are actuated as soon as the upstream-arranged optical sensor device has recognized the foreign substances. The blast emanating from the nozzles blows the fiber tufts--with which the foreign substances are commingled--into a collecting bin. The other, non-contaminated good-fibers are admitted into a collecting funnel and are advanced therefrom to a subsequent cleaning machine. It is a disadvantage of such a conventional arrangement that the conveying device requires a substantial technical and constructional outlay. It is a further drawback that in the known method the optical sensor device operates only separately so that it cannot affect other devices and machines of the fiber cleaning line.